File Preview and Download Using LWC

You will learn the following things

Component Creation
Fetching file Details by sending recordId to Apex
Rendering Data and making it Downloadable
Preview of file on button click
Navigation in LWC

Video Tutorial

Code

Create Lwc component filePreviewAndDownloads and add the following code to the respective files.

filePreviewAndDownloads.html

<template>
    <lightning-card title="File Preview and Download">
         <template for:each={filesList} for:item="file">
             <div key={file.value} class="slds-box">
                 <div class="slds-grid slds-wrap">
                     <div class="slds-col slds-large-size_4-of-12 slds-medium-size_4-of-12 slds-size_12-of-12">
                       <p><strong>FileName - </strong>{file.label}</p>
                     </div>
                     <div class="slds-col slds-large-size_4-of-12 slds-medium-size_4-of-12 slds-size_12-of-12">
                       <a href={file.url} download>Download</a>
                     </div>
                     <div class="slds-col slds-large-size_4-of-12 slds-medium-size_4-of-12 slds-size_12-of-12">
                       <lightning-button label="Preview" 
                       variant="brand"
                      data-id={file.value}
                      onclick={previewHandler}
                       ></lightning-button>
                     </div>
                   </div>
             </div>
         </template>
    </lightning-card> 
    
 </template>

filePreviewAndDownloads.js

import { LightningElement, api, wire } from 'lwc';
import getRelatedFilesByRecordId from '@salesforce/apex/filePreviewAndDownloadController.getRelatedFilesByRecordId'
import {NavigationMixin} from 'lightning/navigation'
export default class FilePreviewAndDownloads extends NavigationMixin(LightningElement) {

    @api recordId='0010o00002ng22vAAA'
    filesList =[]
    @wire(getRelatedFilesByRecordId, {recordId: '$recordId'})
    wiredResult({data, error}){ 
        if(data){ 
            console.log(data)
            this.filesList = Object.keys(data).map(item=>({"label":data[item],
             "value": item,
             "url":`/sfc/servlet.shepherd/document/download/${item}`
            }))
            console.log(this.filesList)
        }
        if(error){ 
            console.log(error)
        }
    }
    previewHandler(event){
        console.log(event.target.dataset.id)
        this[NavigationMixin.Navigate]({ 
            type:'standard__namedPage',
            attributes:{ 
                pageName:'filePreview'
            },
            state:{ 
                selectedRecordId: event.target.dataset.id
            }
        })
    }
}

filePreviewAndDownloads.js-meta.xml

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata">
    <apiVersion>49.0</apiVersion>
    <isExposed>true</isExposed>
    <targets>
        <target>lightning__RecordPage</target>
    </targets>
</LightningComponentBundle>

Create an Apex class filePreviewAndDownloadController.cls and add the following code to the file.

filePreviewAndDownloadController.cls

public with sharing class filePreviewAndDownloadController {
    @AuraEnabled(cacheable=true)
        public static Map<ID, String> getRelatedFilesByRecordId(String recordId) {
            // Get record file IDs        
            List<ContentDocumentLink> files = [SELECT ContentDocumentId FROM ContentDocumentLink WHERE LinkedEntityId = :recordId];
            List<ID> fileIDs = new List<ID>();
            for (ContentDocumentLink docLink : files) {
                fileIDs.add(docLink.ContentDocumentId);
            }
     
            List<ContentVersion> docs = [SELECT ContentDocumentId, FileExtension, Title 
                FROM ContentVersion WHERE ContentDocumentId IN : fileIDs];
            Map<ID, String> mapIdTitle = new Map<ID, String>();
            for (ContentVersion docLink : docs) {
                mapIdTitle.put(docLink.ContentDocumentId, docLink.Title);
            }
            return mapIdTitle;
        }
}